Process of purifying tar acids



Patented Nov. 17, 1942 2302,600 PROCESS OF PURIFYING TAR ACIDS FrancisE. Cislak and Arthur Leonard Kramfelder, Indianapolis, Ind., assignorsto Reilly Tar & Chemical Corporation, Indianapolis, Ind., a corporationof Indiana No Drawing. Application October 7, 1940, Serial No. 360,134

12 Claims.

This invention relates to a process of refining tar acids. Morespecifically it relates to a process for the removal of theobjectionable odor possessed by commercial tar acids, such as phenols,cresols, xylenols, and the like.

Tar acids as normally produced, as from coal tar or from petroleum,possess a disagreeable and for some purposes an objectionable odor.

.The exact nature of the impurities causing the odor is not known. Thereis no doubt,'however, that some of the odor-producing impurities aresulfur-containing compounds, such as thiophenol, thiocresols,mercaptans, and organic sulfides.

It is the object of this invention to produce tar acids-phenols,cresols, xylenols, and the like-having no objectionable or disagreeableodors.

We have found that tar acids free from objectionable and disagreeableodors can be produced by refluxing the crude material with a smallproportion of alkali metals, alkali metal oxids, or alkali metalhydroxides, at a higher pressure, of the order of atmospheric pressure,and then distilling the refluxed acids under reduced pressure, by whichwe mean at less than atmospheric pressure.

Refluxing of the crude tar acids with the alkali metals or alkali metaloxides or hydroxides at atmospheric pressure followed by distillation atatmospheric pressure does not give satisfactory results. Distilling thecrude tar acids under a high vacuum without previously refluxing'them ata higher pressure with alkali metals, oxides,

or hydroxides does not give satisfactory results.

It is'only by first refluxing the crudeacids with 5 the alkali metals,oxides, 0r hydroxides at a higher pressure, or heating the crude acidswith the alkali-metals, oxides, or hydroxides to a temperature at whichrefluxing occurs at atmospheric pressure but avoiding actual refluxingby using a pressure sufficiently high to prevent boiling, and thendistilling them under reduced pressure, that tar acids of good odor canbe obtained. v The examples given below illustrate the manner in whichour invention may be practiced.

Example 1.Two hundred grams of dry, crude, coal tar phenol is heated toabout 100 C., and 0.75-l.5 grams of metallic sodium is added. Thetemperature of the phenol is then gradually raised. When the sodium hascompletely dissolved in the phenol the solutionis refluxed forapproximately four to six hours, at or near atpenol is distilled underreduced pressure mm. to 70 mm. of mercury).

The resulting phenol has a good, clean, sweet, non-sulfur odor.

Example 2.-Two hundred fifty grams of crude cresylic acid is heated toabout 100 C., and 1.5 to 2.5 grams of metallic sodium is added. Afterthe sodium has dissolved in the cresylic acid the solution is refluxedfor five to seven hours, at a pressure of 700 to 800 mm. of mercury. Atthe conclusion of the reflux period the cresol is distilled under vacuum(desirably below mm. mercury pressure).

The resulting cresylic acid has a good, clean, sweet, non-sulfur odor.

Example 3.-To 275 grams of dry, crude, undistilled coal tar acid, (thewhole acid, a mixture of many components,) is added from 0.50 gram to1.25 grams of metallic sodium. The acid is warmed to about 100 0. eitherbefore, during, or after the addition of the sodium. When the metallicsodium has dissolved, the solution is refluxed for five to eight hours.At the end of the reflux period the acid is distilled under a reducedpressure (10 mm. to 70 mm. mercury). The first of acid recovered by thevacuum distillation has a clean, sweet, non-sulfur odor. The last partof the distillate (17% or so).possesses a very slight sulfur odor.

Instead of sodium in the procedure of the foregoing examples we can usepotassium or lithium; or we can use solid sodium or potassium hydroxideor oxide.

The above examples are merely illustrative of the way in which ourinvention may be practiced. They are not to be construed to limit ourinvention in any way.

In the examples given above the preferred pressure for the vacuumdistillation is indicated as from 10 to 70 mm. of mercury. But we arenot restricted to operating between these pressure limits. We have foundthat good results can be obtained when the vacuum distillation iscarried out at somewhat higher pressures, such as mm. of mercury. It hasbeen our experience, however, that the lower the pressure under whichthe distillation is carried out the better the results. We, therefore.prefer to perform the vacuum distillation at as low a pressure as isfeasible,

Similarly, in these examples we have indicated that the refluxing withalkali is done at or near atmospheric pressure. The refluxing pressuremay be somewhat higher or lower than mospheric pressure. After thisreflux period the 55 that; but should not be high enough to causematerial decomposition of the tar acids, as indicated by the formationof tarry deposits during the vacuum-distilling operation, nor low enoughto cause failure of the reaction with the alkali. The desirable range ofrefluxing pressure, and so of refluxing temperature, varies with the taracid being treated, but for best results the refluxing pressure isfairly close to atmospheric pressure.

Instead of refluxing as described in the examples, we may heat the taracids with the alkali metal or oxide or hydroxide to about thetemperature at which refluxing occurs at atmospheric pressure but avoidactual refluxing by using a pressure sufficiently high to preventboiling.

We claim as our invention:

1. The method of purifying tar acids, which comprises refluxing the taracids at or near atmospheric pressure with an alkaline substance of theclass consisting of alkali metals, alkalimetal oxides, and alkali-metalhydroxides, with retention of substantially all the tar acids, and

then distilling off the tar acids under less than atmospheric pressure.

2. The method of purifying tar acids, which comprises heating the taracids with an alkaline substance of the class consisting of alkalimetals, alkali-metal oxides, and alkali-metal hydroxides, to about thetemperature at which refluxing of the tar acids occurs at atmosphericpressure, with retention of substantially all the tar acids, and thendistilling off the tar acids under less than atmospheric pressure.

3. The method of purifying tar acids, which comprises refluxing the taracids at or near atmospheric pressure with an alkaline substance of theclass consisting of alkali metals, alkalimetal oxides, and alkali-metalhydroxides, with retention of substantially all the tar acids, and thendistilling off the tar acids under a pressure of not more than mm. ofmercury.

4. The method of purifying tar acids, which comprises heating the taracids with an alkaline substance of the class consisting of alkalimetals, alkali-metal oxides, and alkali-metal hydroxides, to about thetemperature at which refluxing of the tar acids occurs at atmosphericpressure, with retention of substantially all the tar acids, and thendistilling off the tar acids under a pressure of not more than 70 mm. ofmercury.

5. The process of purifying tar acids as set forth in claim 1, in whichthe tar acid is phenol. 6. The process of purifying tar acids as setforth in claim 2, in which the tar acid is phenol. 7. The process ofpurifying tar acids as set forth in claim 3, in which the tar acid isphenol. 8. The process of purifying tar acids as set forth in claim 4,in which the tar acid is phenol. 9. The process of purifying tar acidsas set forth in claim 1, in which the tar acid is cresylic acid.

10. The process of purifying tar acids as set.

